Halogenoalkanes practise questions
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State the benefit to life on Earth of ozone in the upper atmosphere.
Absorbs (harmful) ultraviolet / uv (light / radiation)
A typical refrigerator contained 0.50 kg of CFC-11 (Mr = 137.5). One molecule of CFC-11 causes the destruction of approximately 100 000 molecules of ozone. Use these data to estimate the number of molecules of ozone that can be destroyed by 0.50 kg of CFC-11 Give your answer in standard form. The Avogadro constant, L = 6.022 × 1023 mol–1
amount of CFC-11 = 500/137.5 ( = 3.64) mol molecules of O3 = 3.64 x 100,000 x 6.022 x 1023 = 2.19 x 10^29
Suggest one reason why the use of CFCs was not restricted until several years after Rowland and Molina published their research.
One of these reasons: * lack of evidence that ozone was being depleted * lack of alternatives to CFCs * commercial interest to continue to use CFCs * hard to obtain international agreement
CFC-11 is a greenhouse gas that can contribute to global warming. State and explain how CFC-11 is able to contribute to global warming
M1 absorbs infrared radiation M2 molecule has polar bonds
Give the IUPAC name of CH3CH2CN(triple bond CN)
Propanenitrile
Q6. Which compound can react with ammonia to produce propylamine? A CH3CH═CH2 B CH3CH2CH2OH C CH3CH2CH2Br D CH3CH2CH3
C CH3CH2CH2B
Which compound could not be produced by reacting 2-bromo-3-methylbutane with sodium hydroxide? A 2-methylbut-1-ene B 3-methylbut-1-ene C 2-methylbut-2-ene D 3-methylbutan-2-ol
Q7. A 2-methylbut-1-ene
Explain why D reacts more quickly than A with dilute aqueous sodium hydroxide at the same temperature. (D= C-Br, A=C-Cl)
C–Br is weaker than C–Cl or C–Br has lower bond enthalpy than C–Cl or C–Br breaks more easily C–Cl
When 2.0 cm3 of 1-bromo-2-methylpropane (Mr = 136.9) were reacted with an excess of sodium hydroxide, 895 mg of 2-methylpropan-1-ol (Mr = 74.0) were obtained. The density of 1-bromo-2-methylpropane is 1.26 g cm−3 Calculate the percentage yield for this reaction.
Amount 1-bromo-2-methylpropane (= (2 × 1.26) / 136.9 = 2.52/136.9) = 0.0184 mol Correct answer scores 3 marks; answer to at least 2sf and any individual marks for M1/2 should be at least 2sf; answers that are a factor of 10x out score 2; 1 M2 mass of 2-methylpropan-1-ol expected (= 0.0184 × 74.0) = 1.36 g Allow ECF through the question 1 M3 % yield = 100 × (0.895/1.36) = 65.7% (65-67%)
State how the graph shows that the rate of reaction of 1-iodobutane is faster than the rate of reaction of 1-bromobutane. State why the rates are different
M1 Iodide ions are produced more rapidly than bromide ions or gradient (of iodide ions graph) is steeper M2 C-I is weaker than C-Br or C-I has lower bond enthalpy than C-Br or C-I breaks more easily than C-Br
Several saturated halogenoalkanes contain 17.8% carbon, 3.0% hydrogen and 79.2% bromine by mass. Calculate the empirical formula of these compounds. Give the IUPAC names of two saturated halogenoalkanes that have this empirical formula.
M1 divide %s by relative atomic masses M2 (1.48 : 3.00 : 0.99 = 3 : 6 : 2) empirical formula = C3H6Br2 M3,4 any 2 of: 1,1-dibromopropane 1,2-dibromopropane 1,3-dibromopropane 2,2-dibromopropane
1-iodopropane is a liquid at room temperature. Calculate the number of molecules in 5.0 cm3 of 1-iodopropane (Mr = 169.9). Give your answer in standard form. For 1-iodopropane, density = 1.75 g cm–3 The Avogadro constant, L = 6.022 x 1023 mol–1
M1 amount of 1-iodopropane =5x1.75/169.9 (= 0.0515 mol) Allow ECF from M1 to M2 based on an attempt to find the amount of 1-iodopropane in moles using the Mr 1 M2 number of molecules = M1 × 6.022 × 1023 = 3.1(0) − 3.13(144) × 1022
In an experiment, 10.3 g of 1-iodopropane (Mr = 169.9) are reacted with an excess of ammonia. 2.3 g of propylamine (Mr = 59.0) are produced. Calculate the percentage yield in this experiment.
M1 amount of propylamine = (= 0.0390 mol) AND amount of 1-iodopropane = (= 0.0606 mol) Allow ECF from M1 to M2 1 M2 % yield = = 63.9 to 64(.4 %)
Define the term stereoisomers.
compounds with the) same (molecular and) structural formula but (Different molecules
A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane. The suggested method is: * add equal volumes of the three halogenoalkanes to separate test tubes * add equal volumes of aqueous silver nitrate to each test tube * record the time taken for a precipitate to appear in each test tube. State and explain the order in which precipitates appear.
Silver iodide then silver bromide then silver chloride Allow yellow then cream then white Allow iodide/AgI then bromide/AgBr then chloride/AgCl Allow iodo(butane) then bromo(butane) then chloro(butane) Ignore iodine then bromine then chlorine 1 bond strength C−I < C−Br < C−Cl